Black Friday: Tornado in Canada "The roof was caving in and I thought I was going to die. It was like your worst nightmare!" said Mary Grandish. Most people think they will die when they see,or hear of a tornado heading their way. Although all the details of the formation of a tornado are not yet understood, it is known that tornados are the result of great instability in the atmosphere and often appear during severe thunderstorms (see appendix #1 for a scientific explaination on how it really starts). Strong updrafts present in severe thunderstorms result in a rotational momentum. Falling rain and/or snow probably drags air from aloft